The present invention is related to an apparatus and method for the extraction of contaminants from subsurface soils. In particular, the present invention provides an apparatus and method for introducing air into a zone of liquid-phase contaminants in subsurface media to thereby increase contaminant vapor concentrations being extracted from the well in the form of volatilized contaminant.
Vacuum extraction of volatile organic compounds from soil has been known as a popular remediation technique. Typically, a recovery well is installed in the contaminated region to recover subsurface vapors and gases by applying a vacuum to the well via a vacuum pump at the ground surface, for example. The vacuum pump can exhaust vapors to the atmosphere or to contaminant recovery equipment such as filter equipment or a combustion chamber depending upon the contaminants and their concentrations.
Contamination of the subsurface soils with potentially hazardous materials happens as a result of spills, leakage from storage facilities, or surface discharges. The contaminants may eventually percolate into the ground water posing a health threat to drinking water supplies. It is desirable to be able to remove the contaminant from subsoil regions as quickly as possible. Currently, known methods of contaminant removal take too long and are not as successful as the industry would like in connection with removing all or substantially all of the contaminant at a particular site.
The present invention is concerned with removing liquid-phase hydrocarbons floating on top of the water table. The present invention provides a method and apparatus for removing volatile and semi-volatile contaminants from any depth without expensive excavation of a large amount of contaminated soil or rock. The equipment used to perform the present invention can be conventional equipment, controlled at the surface of the ground. With the exception of the well casing and associated components which will be described hereinafter, there is very little disruption of the subsurface media with the present invention.
The present invention includes the steps of directly removing vapor-phase, liquid-phase, and adsorbed-phase volatile and semi-volatile organic compounds from primarily porous layers of soil or rock by vacuum extraction. Once the contaminant is collected at the surface it may be treated at the site or treated elsewhere and later disposed of in a proper manner.
According to the present invention one or more wells are drilled into the subsurface media in the contaminated area. The well may be constructed so that liquid-phase hydrocarbons may flow into the well as gases. The upper portion of the well is preferably impervious, whereas the lower portion of the well is preferably perforate. The lower portion of the well may be surrounded by an air permeable material, such as gravel. The upper portion of the well may be surrounded with a material of low vapor permeability to inhibit leakage of air from the surface of the ground to the lower perforate portion of the well. The upper end of the well is preferably connected to a suitable vacuum source, for example an air blower or vacuum pump, to create a negative pressure (vacuum) in the well, thus inducing flow of air containing gaseous phase contaminants directly into the perforate lower portion of the well. The exhaust of the air blower or vacuum pump may be connected to a suitable recovery or treatment system.
Furthermore, the well of the present invention would include an inner tube which would descend from the surface to the zone of liquid-phase hydrocarbons in the subsurface media, above the water table. At the surface air may enter the tube and flow down through the tube such that air exits the tube in the region of the liquid-phase hydrocarbons. Resulting bubbles created in the liquid-phase hydrocarbons greatly increase the contaminant evaporation rate of the liquid-phase hydrocarbons to assist in the removal of liquid-phase contaminant.
According to the invention contaminants are removed from the subsurface media of a contaminated underground area by first establishing a borehole from the surface of the ground within the contaminated area by drilling or driving a borehole in any conventional manner. The borehole would preferably extend into the water table. A conduit or well casing is inserted in and may be radially inwardly spaced from the borehole so that a ring or annular zone is defined between the borehole and the conduit. The conduit preferably has a perforate lower portion so that fluids can flow into its interior, whereas the upper portion of the conduit is impervious. The annular zone defined above may be filled with a loose, fluid permerable, fill material which extends substantially up to the upper end of the perforate lower portion of the conduit. The annular zone above the perforate lower portion of the conduit may be packed with a second fill material of low permeability to impede air flow from the ground surface downward toward the lower portion of the borehole. An air tube may then be installed within the conduit descending through the sealed cap at the ground surface to the liquid-phase hydrocarbons in the perforate lower portion of the conduit. A vacuum inside the conduit created by the vacuum pump draws air from the atmosphere through the air tube down into the liquid-phase hydrocarbons. Resulting air bubbles travel upwards through the liquid-phase hydrocarbons and become saturated with hydrocarbon vapors. As the hydrocarbon vapor-laden bubbles reach the liquid surface, they are drawn to the upper end of the conduit for recovery or discharge.